1. Field of the Invention
This invention relates to pneumatic motors for rock drills and the like and, more specifically, relates to such motors which are valveless and have improved means for distributing motive fluid so as to cause the desired reciprocating movement of a hammer piston within the cylinder.
2. Description of the Prior Art
It has been known to provide pneumatically actuated apparatus wherein a piston is caused to reciprocate within a cylinder under the influence of pressurized air thereby causing the piston to deliver a series of impact blows to a tool such as a striking bar, a tappet or drill rod. In such systems, initial propulsion of the piston results from the influence of the pressurized motive fluid with the subsequent travel being due to inertia of the piston coupled with residual pressure of the motive fluid. When the piston has reached the limit of its travel in a first direction, motive fluid is delivered to the opposite side of the piston causing it to reciprocate in the reverse direction initially under the influence of the pressurized motive fluid and subsequently under the influence of inertia coupled with residual pressure from the motive fluid.
Various internal means for alternately conducting the pneumatic fluid to opposite sides of the piston head have been known. It has been known to employ various passageway constructions in combination with separate valve members. See, for example, U.S. Pat. Nos. 622,576; 705,436; 727,954 and 1,800,344. It has also been known to provide systems wherein the cylinder profile cooperates with passageways in such a fashion as to establish a valving action. See, for example, U.S. Pat. Nos. 726,074; 742,934; 1,114,075; 1,128,416; 1,660,201; 1,726,352; 2,722,918; 3,329,068 and U.S. Pat. No. Re. 28,859.
One of the problems encountered with prior art constructions has been the inherent complexity and the need to engage in extensive machining operations in order to provide the desired passageways for transport of the motive fluid. Such designs not only contribute to complexity of manufacture and repair, but also increase the product cost.
There remains a very real and substantial need for improved pneumatic motors which are of relatively simple design and yet provide efficient operation over a prolonged period of use.